System for stereo separation ratio control, elimination of cross-talk and the like



Feb. 23, 1965 SGAL ,l70,99l

R. GLA 3 SYSTEM FOR STEREO SEPARATION RATIO CONTROL, ELIMINATION OF CROSS-TALK AND THE LIKE Filed Nov. 27, 19s:

g5 INPUT LEF'L INPUT l I I6 I LEFT l MIXER u T I UNITY GAIN PHASE REVERSE FIG! FIG 2 T T f' INVENTOR, RIGHT A5 RALPH GLASGAL, Q

' J BY 4 L ATTORNEY.

United States Patent 3 170 991 SYSTEM FOR srnand sEP TroN RATIO CON- {fig ELIMIN ATION or CROSS-TALK AND nan Ralph Glasgal, 39-43 46th St., Long Island City, NY. Filed Nov. 27, 1963, Ser, No. 327,876 4 Claims. 01. 179-1 The present invention relates to electronic stereophonic apparatus by which two electronic signals are simultaneously translated into sound to attain a stereophonic effect and more particularly to a stereo dimension control therefor. This application is a continuation-in-part of my application filed February 1, 1961 under Serial No. 86,480 which is now abandoned upon the filing of this application.

stereophonic apparatus uses a left signal and a right signal. It is known that the directional and separation elfects of stereophonic sound reproduction depend upon the ratio of the difference to the sum of said signals. It is therefore the principal object of this invention to provide a novel and improved means to adjust such separation ratio by a simple manipulation at the receiver so that a listener may adjust the stereo dimension and separation effects to his own taste at will and over a wide range.

Another object thereof is to provide a novel and improved stereo dimension control of the character mentioned, which is simple in construction, reasonable in cost and efiicient in carrying out the purposes for which it is designed.

Other objects and advantages will become apparent as this disclosure proceeds.

equal two, we should have a new left signal L and a new right signal R, such that:

L-R=2(LR) and L+R=L' R' Solving these equations for the values of L and R, we obtain Where K is a constant, that Similar results ensue upon any change of the value of said ratio between the limits of zero and plus infinity. The above shows that to increase the separation ratio,

it is only necessary to add to each signal L and R respectively, an out-of-phase signal from the other. Likewise, to decrease the separation ratio, it is only necessary to add to each signalL and R respectively, an in-phase signal from the other.

I will now set forth a preferred embodiment of thisinvention for which I shall refer to the accompanying drawing forming part of this specification, in which drawing, corresponding parts in all the views are indicated by similar characters of reference.

FIG; 1 is a block diagram of a stereo separation ratio control system in accordance with this invention.

For the practice of this invention to change the separation ratio, I add to each signal an out-'of-phase signal from the other.

To show that this will accomplish the required purpose, I present the following equations. The left and right signals are designated by the letters L and R respectively. The L and R signals may be similar or completely random with respect to each other in amplitude, frequency, or both. I first form the instantaneous sum and difference signals (L +R,), (L R where the subscript i indicates the instantaneous value of the signal, and the sum and difference are formed by the algebraic addition of instantaneous values. I now define the separation ratio indicated by the notation SR as the ratio of the R.M.S. value of the difference signal to the R.M.S. value of the sum signal, thus:

It has been established experimentally that the value of this ratio is proportional to the separation heard by the listener during stereophonic reproduction. For a separation ratio of one, all the sound will seem to emanate from two point sources to the left and right of the listener. For a separation ratio of zero, all the sound seems to emanate from a point directly in front of the listener. For a separation ratio greater than one, the sound emanates from points further apart than the reproducing loudspeakers.

Now suppose that we have a left and a right signal whose separation ratio is one and it is desired to increase this separation ratio so that the sound will appear to have greater dimensionality. For such, the said ratio is set equal to some number greater than one, choosing two for example. Now the ratio reads:

where the primed values refer to the original signals whose separation ratio we know to be one. For this ratio to FIG. 2 shows a Wiring diagram for the same.

In the drawing, in the electronic system shown, a first unity gain phase reverse amplifier 15 and a second unity gain phase reverse amplifier 15, invert the left and right input signals respectively without changing their magnitudes. Thus both polarities of the left and right input signals L, L, R, 'R are available at the input and output terminals of the unity gain phase reverse amplifiers 15 'and 15'. The +L signal is applied to one end of the resistance "r of a potentiometer 17. The L signal from the output of the unity gain phase reverse amplifier 15, is applied to the other end of the same resistance r. Thus the movable potentiometer contact 19 will vary in potential from l-L to L, as it is moved from one end of the resistance r to the other end thereof. At some point near the middle, the potential must be zero. At this point a tap is made and connected directly to ground. This connection isnot essential to the operation of this invention, but does result in improved potentiometer tracking linearity, stability and reproducibility. The voltage on the movable potentiometer contact 19 is the output of the potentiometer. This voltage is now added to the plus R signal in a mixer stage 16, to produce the right output signal. 7

Similarly, the plus R signal is connected to one end of a potentiometer resistor r. This potentiometer 17' is preferably mechanically coupled to the potentiometer 17, so that the resistors r and r track identically together over their entire resistance range. The plus R connection is made to the same terminal of the resistor r' as the plus L Signal of the resistor r. The minus R signal from the output of the unity gain reverse amplifier 15' is connected to the other end of the resistor 1''. Thus the movable potentiometer contact 19 will vary in potential from plus R to minus R as it is moved from one end of the resistor r to the other end thereof. The voltage on the movable potentiometer contact 19 is the output of the poteniometer 17. This output voltage is now added to the plus L signal in a mixer stage 16 to produce the left output signal. It is readily apparent from the above disclosure that the operation of said system is such that to each of the signal inputs L and R, there is added an out-of-phase or in-phase signal from the other, depending on which side of the center tap the potentiometer slider is set. The range of the right signal output is R plus L through R 3 minus L. The range of the left signal output is L plus R through L to L minus R.

Although I have set forth the use of this system for the adjustment of the separation ratio in stereophonic apparatus, it is readily seen that this control'can be used to counteract cross talk in any audio system.

It is evident that the movable taps 19, 19' need not be ganged so that variations in results can be achieved as may be required by any particular employment of the system taught herein. It is also true that the center taps of the potentiometers, indicated at 18, 18, need not be'grounded or used and that indeed such taps may be omitted entirely without negating the value of this invention or changing its principle of operation. These taps may also be returned to a D.C. potential other than ground if desired.

The apparatus 15, 16, 16', each comprises a tube, a source of potential and various resistances and condensers. Anologous components are of the same value in each, so values given for one will sufiice for all which are in similar arrangement in FIG. 2. As an example of values of the various components for a practical system for stereo dimension control, in which number or letter symbols are well known in the art, are:

Each tube 20 is l2AX7, B plus is 300 v., the resistance 21 is 220K, the condenser 22 is 0.1 mfd., the resistance 23 is 2.2K, the condenser 24 is 50 mfd. 3 v., each of the potentiometer resistance r and r is 500K and all the other resistances 25, 26, 27 and 28 are 470K.

An illustrative circuit of the system is shown in FIG. 2. Blocks 15, 15, 16 and 16 are identical unity gain anode followers with a 470K input impedance and low output impedance. The tube 20 is a triode amplifier. The resistance 23 is connected from the cathode of the tube 20 to ground. This resistor provides operating bias for the tube. The capacitor 24 between cathode and ground, serves to bypass the resistor 23 and thereby prevent the loss of gain and the increase in output impedance that would occur if the resistor 23 .were not bypassed by the capacitor 24. The resistor 21 serves as a plate load resistor between the B-plus voltage and the plate of tube 20. The resistor 21 provides a load across which an output voltage can be developed. The B-plus supply is necessary to furnish the power for the amplification process. The capacitor 22 couples the signal at the plate of the tube 20 to potentiometer resistance component and to the feedback resistor 25, and keeps D.C. from flowing in these circuit elements. The resistor 25 is a feedback resistor and couples the plate voltage of the grid of the tube 20. The resistor 26 acts as a load for the resistor 25, increases the input impedance to a level where the input will not load external signal sources, and sets the gain of the anode follower in concert with the resistor 25. The function of the resistor 26 is performed in the mixer 16 and 16' by the resistors 27 and 28. Two resistors are used here so that two signals may be applied to the anode follower at the same time. The output of the anode follower mixer will be the instantaneous sum of the voltages present at the exterior ends of the resistors 27 and 28. The left input signal is connected to the resistor 26 of anode follower 15' and to the resistor 28 of the mixer 16. In addition, the left signal is connected to the low side or end of the potentiometer resistor r. The right signal input is connected to the low side or end of the potentiometer resistor r. The output of the anode follower 15 is connected to the high side or end of the potentiometer resistor r and the output of the anode follower 15' is connected to the high side of end of the potentiometer resistor r. The sliding contact 19 of the resistor r is connected to resistor 27 of the mixer 16 and the sliding contact 19' of the resistor r is connected to the resistor 27 of the mixer 16. The right output signal is taken from the exterior end of the capacitor 22 of the mixer 16. The left output signal is taken from the exterior end of the capacitor 22 of the mixer 16'.

The sliders 19, 19 of both potentiometers are ideally coupled mechanically so that they move together in the same direction. The center taps 18, 18' are connected to ground. These taps are located at the electrical center of the resistance element and such tap location should coincide with the midpoint of the mechanical movement of the sliders, as well. The resistance element of the respective potentiometers is made with a linear taper. That is, the change in resistance for a given movement of the slider is a constant value throughout the range of operation.

This invention is capable of numerous forms and various applications without departing from the essential features herein disclosed. It is therefore intended and desired that the embodiment shown shall be deemed merely illustrative and not restrictive and that the patent shall cover all patentable novelty herein set forth; reference being had to the following claims rather than to the specific description herein to indicate the scope of this invention.

I claim:

1. A system of the character described, utilizing first and second input signals, first and second potentiometers, each comprising a resistance and a tap movable therealong, first and second mixers, each having an output terminal and two input terminals and first and second unity gain phase reversers, wherein the resistance of the first potentiometer is connected across both phases of the first input signal and the resistance of the second potentiometer is connected across both phases of the second input signal, the movable taps of said first and second potentiometers being electrically connected as inputs to said first and second mixers respectively, a first input signal electrically connected to the input terminal of the first phase reverser and the second mixer, a second input signal electrically connected to the input terminal of the second phase reverser and to the first mixer; the output signal of the first mixer being the new modified second signal and the output signal of the second mixer being the new modified first signal of said system.

2. A system as defined in claim 1, wherein said movable taps are in ganged relation.

3. A system as defined in claim 1, wherein said potentiometer resistances, each have a mid point tap connected to a D.C. potential, respectively.

4. A system as defined in claim 3, wherein the D.C. potential is ground.

No references cited.

ROBERT H. ROSE, Primary Examiner. 

1. A SYSTEM OF THE CHARACTER DESCRIBED, UTILIZING FIRST AND SECOND INPUT SIGNALS, FIRST AND SECOND POTENTIOMETERS, EACH COMPRISING A RESISTANCE AND A TAP MOVABLE THEREALONG, FIRST AND SECOND MIXERS, EACH HAVING AN OUTPUT TERMINAL AND TWO INPUT TERMINALS AND FIRST AND SECOND UNITY GAIN PHASE REVERSERS, WHEREIN THE RESISTANCE OF THE FIRST POTENTIOMETER IS CONNECTED ACROSS BOTH PHASES OF THE FIRST INPUT SIGNAL AND THE RESISTANCE OF THE SECOND POTENTIOMETER IS CONNECTED ACROSS BOTH PHASES OF THE SECOND INPUT SIGNAL, THE MOVABLE TAPS OF SAID FIRST AND SECOND POTENTIOMETERS BEING ELECTRICALY CONNECTED AS INPUTS TO SAID FIRST AND SECOND MIXERS RESPECTIVELY. A FIRST INPUT SIGNAL ELECTRICALLY CONNECTED TO THE INPUT TERMINAL OF THE FIRST PHASE REVERSER AND THE SECOND MIXER, A SECOND INPUT SIGNAL ELECTRICALLY CONNECTED TO THE INPUT TERMINAL OF THE SECOND PHASE REVERSER AND TO THE FIST MIXER; THE OUTPUT SIGNAL OF THE FIRST MIXER BEING THE NEW MODIFIED SECOND SIGNAL AND THE OUTPUT SIGNAL OF THE SECOND MIXER BEING THE NEW MODIFIED FIRST SIGNAL OF SAID SYSTEM. 